One of the most feared sports and work injuries is a torn anterior cruciate ligament or ACL. It's the tough piece of tissue that keeps the knee from bending sideways when you plant your foot and pivot.

Nobody is exactly sure of the best way to treat a torn ACL. Yet every year, at least 200,000 Americans undergo ACL reconstruction, in which the ACL is restored with tendon grafts. Most patients undergo this surgery soon after their injury.

But that may not be the best strategy for everyone, suggests a clinical trial by physiotherapist Richard B. Frobell, PhD, of Sweden's Lund University, and colleagues.

ACL: To Operate or Not?

Frobell's team randomly assigned 121 young, active adults -- many of them highly competitive, non-professional athletes -- to two different treatments.

Both groups underwent a highly structured rehabilitation program in which they worked up from improving balance and coordination to knee strengthening exercises.

One group underwent ACL reconstruction within 10 weeks of injury. But the other group delayed ACL reconstruction until it became obvious they needed it -- or until they healed.

Two years later, both groups had good results. Neither treatment strategy was better than the other. But there was one big difference: 60% of those who delayed surgery found they never needed the operation.

"A lot of people say you need ACL surgery if you want to return to sports. But our results show we might be better off if we start with rehabilitation," Frobell tells WebMD. "Then we can reduce the number of people needing surgery."

Many Factors Involved in ACL Treatment

Mayo Clinic orthopaedic surgeon Bruce A. Levy, MD, is full of praise for the Frobell study. But he warns that some patients risk further damage to their knees by delaying ACL reconstruction.

The injury that rips the ACL may damage other parts of the knee, particularly the meniscus -- the piece of cartilage that cushions the bones of the knee.

"If you have a large meniscus tear and you fix the meniscus and not the ACL, there is a very high likelihood the ACL will fail," Levy tells WebMD.

On the other hand, a patient who is a relatively low-level recreational athlete -- Levy offers the example of a 35-year-old cyclist -- may be better off with bracing and rehabilitation. Only if such patients have further ACL problems would surgery be the preferred option. But a collegiate soccer player might not be able to return to play without ACL reconstruction.

"When a patient presents with an ACL tear in the knee, we have a long discussion with the patient and family on the pros and cons of operative and nonoperative treatment," Levy says. "The decision is based on many factors. First and foremost is the patient's activity level, and the sport and work demands the knee would undergo."

Frobell fully agrees with Levy that the study does not give patients or doctors a one-size-fits-all solution to treatment of ACL tears.

"Our study does not answer the question of specifically who needs ACL surgery. It does not look into what factors a patient has to have to need surgery to do well," he says. "We need a lot of more high-quality science in this area."

Some of that data may be coming soon. Levy says he'd like to see how Frobell's patients do in the long term. Frobell says the last patient in the study is just completing five years of follow-up observation. More information is on the way.

The Frobell study, and an editorial by Levy, appear in the July 22 issue of the New England Journal of Medicine.